There's a few other differences in the back end.. fuel tank and mountings, rear shock area is smaller so aftermarket performance shocks may not fit. Rear door stuff and seals, license plate mounts for rear. Vans will also have external hinges, so interior door panels from an 84 sedan will not fit.  Depending on Van year the floor area for the shifter and shifter boot. may be different. Fuel line to rear is longer and if fitting a later engine the return line will need to be fitted.  Firewall area is a little different so mounting holes may be different as well.  But as Willie_B says.. most stuff will be reusable. It's certainly doable.

The estate & panel van have a longer wheel base. All the mechanical parts will fit except the hand brake cable and brake line going to the rear.

I have an '84 mini sedan I've replaced or reconditioned every nut and bolt, rusted panel and all electrics on. Still needs painting though.  I now have a hankering for a mini window van or panel truck and I'm wondering about the availability of replacement parts.  Will most of the same things I replaced on my sedan fit a van or panel?  I'm sure buying one that has already been restored will be way out of my budget range.

Jack